It really isn't all that complicated though, and just takes money to fix the urban planning mistakes that have been made in many metropolitan cities.
Montreal is probably the most livable "big" city in North America, and it's mostly because of three things:
1. Excellent transportation. The metro is for the most part consistent, extremely affordable (it's ~$85/month, and about half that for students and youth), safe, and works as a great mainline transport. Busses are also very frequent - most coming at most 15 minutes apart during regular hours, and usually every half hour or so past 1am. You can get almost anywhere in the city in an hour or less using public transit.
2. Renters are protected. The Regie Du Logement heavily favours renters in housing related disputes, and as such, the prices also favour renters. Most individuals pay $1000 or less in rent, for entirely adequate housing, and if they want to move, it's almost certainly an option.
3. Permissive zoning. With the exception of the downtown core, there are grocery stores and pharmacies everywhere. Combined with depanneurs (corner stores) being within 500m of just about any point in the city, you are never far from milk, eggs, bread, beer, wine, and other necessities. Combined with businesses themselves being able to set up shop nearly anywhere as well. Ground floor business with residential above is the norm for nearly all "main" streets.
Yes, there are difficult things for existing cities to recreate, but it is almost entirely due to poor urban planning choices being made by the municipal (or state/provincial) powers that be.